In revolver firearms, the cylinder has formed therein a plurality of chambers for receiving cartridges. The cylinder rotates in the frame to successively present the chambers to the barrel. Such revolvers have generally been constructed with a clearance space or gap between the rear end of the barrel and the cylinder. After a shot is fired, and the explosion of the propellant material in the cartridge has moved the bullet out of the chamber into the barrel, the expanding hot propellant gases escape through this gap. The expanding propellant gases also contain unburnt powder particles which travel at velocities similar to, or in excess of, the speed of the bullet and tend to erode those portions of the frame upon which they impact. This erosion of the frame causes a weakening of the frame, which can result in the breaking or premature failure of the frame.
The rate of firearm frame erosion is dependant to a large extent on the performance of the cartridge and the hardness of the frame where the particulate contact. By way of example, in a high performance cartridge, e.g., 357 magnum or 32 magnum, the particles travel at speeds of up to 1600 feet per second and will erode the frame away at a much more accelerated rate than a lower performance cartridge such as a 22 caliber round. Additionally, unburnt particulate erosion is much more problematic in softer material frames, e.g., aluminum alloy frames, than in frames with harder material such as stainless steel.
U.S. Pat No. 3,136,084, filed on Mar. 9, 1962, and entitled "Gas Cutting Prevention In Revolver Firearms", attempts to address the problem of frame erosion by providing a hardened portion in the frame adjacent to the gap between the barrel and the cylinder. The hardened portion is integrally formed in the frame by cutting a groove in the inner surface of the top strap that extends over the cylinder and bridges the gap. A heat-treatable alloy, capable of achieving a hardness substantially greater than the remainder of the frame, is welded into the groove to form an insert. Once the firearm is heat-treated to an appropriate hardness, the insert is machined down to be flush with the frame.
However, the additional operations of cutting, welding and re-machining required to form the insert had a prohibitive affect on the production costs of the frame. As a result, very few, if any, firearms were produced with such an insert. Moreover, even the hardened portion of the frame would wear over time, and would be very difficult to service in the field because of the special production tooling required to repair or replace the insert.
There is, therefore, a need for an improved method and apparatus for protecting a firearm frame from erosion from propellant gas and unburnt particulate.